Electron discharge valves



Aug. 18, 1959 w. s. PERCIVAL 2,900,567

ELECTRON DISCHARGE VALVES Filed Sept. 15, 1956 nun! 4 FIG. 2

l I mew 'HSRPCZLUQ/Z United States Patent ELECTRON DISCHARGE VALVES Claims priority, application Great Britain September 15, 1955 2 Claims. (Cl. 31539) This invention relates to electron discharge valves and relates in particular to so called transmission line valves, that is valves in which electrodes are wound so as to form, in conjunction with distributed reactances, electrical transmission lines enabling the valves to operate as distributed amplifiers.

The construction of various forms of transmission line valves are described in United States patent specification No. 2,211,859. Such valves are based upon the principle that a transmission line which is terminated by a substantially non-reflecting termination presents an input impedance which is substantially a pure resistance in a predetermined range of frequencies, so that substantially uniform amplification over a wide range of frequencies can be obtained.

One problem associated with a transmission line valve is that of reducing electrostatic coupling and magnetic coupling between the output and input lines of the valve in order to obtain stability in operation of the valve. Electrostatic coupling can be reduced by employing a screen electrode between the output and input lines, but the problem of magnetic coupling remains. This problem, moreover, becomes more acute at higher frequencies, for example in pulse amplifying arrangements in which frequencies of 1000 mc./s. or more are involved.

The object of the present invention is to substantially reduce the magnetic coupling which may exist between the output and input lines of an electron discharge transmission line valve.

According to the present invention there is provided an electron discharge valve having at least three electrodes, two of said electrodes being inductive and forming respectively, a. transmission line for input signals to said valve and a transmission line for output signals from said valve, and said inductive electrodes being wound to cause the flux linkages between one inductive electrode and difierent parts of the other inductive electrode to be at least partly mutually cancelling, so as to reduce magnetic coupling which would otherwise exist between said inductive electrodes.

In order that the invention may be clearly understood and readily carried into efiect, the invention will be described with reference to the accompanying drawings, in which:

Figure 1 illustrates diagrammatically and in cross-sectional view the arrangements of the electrodes in a pentode valve according to an example of the present invention, and

Figure 2 illustrates symbolically the pentode valve of Figure 1 embodied in a suitable amplifying circuit arrangement.

Referring to Figure 1, reference 1 denotes a long indirectly heated cathode of fiat construction, that is having a substantially rectangular cross-section with one cross-sectional dimension large compared with the other. The cathode is enclosed by a control electrode 2 formed by wire wound on a frame which for simplicity is not ,Patented Aug. 18, 1959 shown but'is composed at least in part of insulating material so that this control electrode forms a coiled grid. The frame for this grid may consist, although for simplicity of illustration they are not shown, of four rods parallel to the cathode and lying adjacent to the edges thereof and the grid is then also substantially rectangular in end view. The number of turns of the coil forming the control electrode may be considerably greater than the number of turns required for the inductance of the input transmission line. for the valve, formed by the control electrode and associated distributed capacities, and in this case, groups of the control electrode wires may be connected in parallel. Surrounding the control electrode are first the screen electrode 3 and the suppressor electrode 4. The anode 5 of the valve consists of two coils connected in parallel and facing the large rectangular sides of the other electrodes as shown in the figure. The anode coils are wound in such sense as to give substantially no magnetic coupling to the control grid. The electrodes are enclosed in a suitable evacuated envelope 15 into which are sealed in known manner terminal leads for the electrodes, and to enable the control electrode and anode lines to be suitably terminated, when the valve is in use, the anode and control electrode coils are connected at both ends to suitable external leads as indicated in Figure 2.

In Figure '2 which illustrates a distributed amplifier stage, references 1 to 5 represent the electrodes described with reference to Figure 1 but for simplicity they are shown in a symbolic manner. References 6 and 7 denote the high tension and grounded lines respectively for the amplifier. The resistor 8 and capacitor 9 constitute a conventional cathode bias circuit for the valve and the suppressor grid 4, which operates in known manner to suppress secondary electron emission from theanode, is connected to the cathode. The screen grid 3, is maintained in conventional manner by the resistor 10 and the capacitor 11, at :a steady potential .to reduce electrostatic coupling between the anode and the control electrode. The two parallel connected coils constituting the anode are connected at one end to the load resistor 12 and at the other to a matching resistor 13, the resistors 12 and 13 having their other ends connected to the line 6. The resistor 14 is a matched terminating resistor for the control grid line.

In operation of the valve described as a distributed amplifier, the signals to be amplified are applied, from a matched source, to one end of the control electrode 2 which in conjunction with the distributed capacities between 2 and the cathode forms one transmission line being terminated by the resistor '14. The input signals therefore proceed along the line and corresponding but amplified signals travel in both directions along the anode coils 5 which in conjunction with the associated capacities with the cathode operate as a pair of transmission lines in parallel, being terminated by the matching resistor 13 at one end and the load resistor 12 at the other. The amplified output signals can be derived moreover from the resistor 12. Since the coils 5 which form the anode are disposed on opposite sides of the control electrode and are wound in opposite senses, flux linkages between the different parts of the anode formed by the coils 5 and the control electrode 2 are substantially mutually cancelling. Therefore feedback from the anode .to the control electrode by virtue of magnetic coupling is substantially eliminated. It is a feature of the valve moreover that the anode coils 5 are sufiiciently remote from one another so that mutual fiux cancellation between them is substantially small whereas their flux linkages with the control electrode are of opposite sense and mutually cancelling.

It will be appreciated that the anode may be wound in other ways than that illustrated in order to reduce the magnetic coupling. For example the anode coil may comprise two parts wound in opposite senses and co-axially disposed, one coil being for example of larger diameter than the other.

What I claim is:

1. An electron discharge valve having. at least three electrodes two of said electrodes being inductive and forming respectively a fiansrnission line for input signals to said valve and a transmission line for output signals from said valve, one of said inductive electrodestbeing formed of different parts and said one inductive electrode being wound to cause the flux linkages between the difierent parts thereof and the other inductive electrode to be at least partly mutually cancelling. i V

2, A valve according to claim 1 wherein said inductive electrodes comprise respectively a control electrode and an anode and the third electrode comprises a cathode, said control electrode comprising a coil wound round the cathode and said anode comprising .two coils disposed on opposite sides of said control electrode, and wound in senses predetermined to cause flux linkage from said coils to said control electrode to be at least partially mutually cancelling.

References Cited in the file of this patent UNITED STATES PATENTS 

